Heavy duty cargo tie-down systems may utilize chains as the tension members and the present invention pertains to systems of this type. Cargo tie-downs of the chain type must use tensioners which are easily operated by inexperienced personnel, must be capable of easily tensioning the chain after the chain has been connected to the tensioner, and the chain must be easily released from the tensioner without having to gradually release the tension.
As chain-type cargo tie-down systems are of a non-elastic character in that the chain does not expand or elongate under tension, the chains of the system must be properly tensioned, and maintain the desired tension, if impacts and jarring are to be avoided due to a tendency for the cargo to shift. Previously, available chain tensioners for tie-down systems have not had the ability to effectively cushion impacts arising from high tension forces imposed upon the tensioner.
A chain tensioner for cargo tie-down systems is shown in the assignee's U.S. Pat. No. 3,601,864 issued Aug. 31, 1971, and while the chain tensioner shown therein solves many of the previous problems, this tensioner is not capable of cushioning impact forces and absorbing high tension impact forces which may damage or render inoperable known chain tensioners.
It is an object of the invention to provide a chain tensioner for cargo tie-down systems which is of concise configuration, may be operated by relatively inexperienced personnel, and is capable of cushioning high tension impact forces.
Another object of the invention is to provide a chain tensioner for cargo tie-down systems capable of cushioning impact forces wherein tightening of the chain may be readily accomplished and the operating characteristics of the tightener may be adjusted by imposing a prestressed condition on the cushioning material.
In the practice of the invention two elongated members are interconnected in a telescoping relationship. The first member includes an outer end upon which a latching head is defined which includes a latch hook pivotally mounted thereon for movement between operative and release positions relative to a grab link defined on the chain being tensioned. The latch hook is held in the operative position by a pivotal detent operated by a release ring rotatably mounted on the latching head having an internal cam cooperating with a pin plate which positions the detent. This structure permits the chain grab link to be readily inserted into the latching head and held therein by the latch hook, or easily released by actuation of the release ring.
A threaded stem non-rotatably extends from the latching head and telescopingly receives the tubular inner end of a second elongated member. The outer end of the second member includes a tension transmitting fitting in the form of a hook wherein the second member may be releasably attached to a fixed bar forming a part of the cargo container, bulkhead or other stationary component.
A housing constituting an enlarged nut is threaded upon the stem threads, and the housing includes an annular chamber in which the second member inner end is received. A radial flange defined on the second member within the housing chamber is in opposed relationship to an adjustable shoulder nut threaded into the housing and defining a portion of the chamber, and an impact cushioning element, in the form of an annular urethane ring, is interposed between the flange and the shoulder nut whereby tension between the first and second members compresses the urethane and relative movement between the flange and housing occurs as the urethane is compressed.
An annular sleeve within the housing chamber of an axial length less than the normal axial length of the urethane cushion surrounds the cushion and is interposed between the flange and housing shoulder nut and will engage these components upon predetermined displacement taking place between the flange and housing during cushioning. The sleeve will prevent excessive deformation and overcompression of the cushion material and permit the apparatus to accommodate very high impact tension forces without damage. The housing shoulder nut is axially adjustable to apply a precompression to the cushion material which will assure the proper orientation of the components, and prevent inadvertent rotation of the housing relative to the stem which would permit the tensioner to accidentally unloosen.
Another improvement in the instant invention pertains to the utilization of a notch defined in the pin plate employed to actuate the latch hook detent. The detent includes an arm extension closely received within a notch defined in the pin plate radially positioned by the release ring, and by confining the detent arm within the notch, a positive actuation of the detent is assured at all locations of rotation of the release ring preventing inadvertent release of the latch hook during operation of the release ring.